If we can re-design everything (not the lib, but the language) allover again from the very beginning , and if we all put an i18n engr's hat on:-) it might be nature to have a 32-bit char instead of the 16-bit (OK, it's totally a difference story if from performance point of view), and then we would not have this kind of trouble at all. The reality is that String is still UTF16 and char based, Unicode supplementary code point support is an add-on, so the default index based iteration is char based. You will have to use those codePointXYZ() to do code point based access. If you consider the replaceAll() is to replace all targeted sub-string, and this sub-string happens to be an empty string in this case, as long as String.substring(i, i+1) works for the index "i" which is in between of two paired surrogates, it is hard to argue that you should not replace that "sub-string" with the replacement. Another "excuse" to back my "not a bug" argument is that as the API doc suggests the String.replaceAll() is simply a wrapper of j.u.regex.Matcher, both Pattern and Matcher class all explicitly documents that they work on "CharSequence", which is pure char based and "does not" know code point (for now, with the new defender method, it might be possible to evolute the CharSequence, if desirable, but that would be a totally different discussion). When I say "work on CharSequence", I'm not saying the Pattern does/should not work on code point, actually the implementation "transfers" all the String based pattern into a code point based pattern before interpreting it, but all code/point (mainly for supplementary) support works on the assumption that you have a "constructor". An empty string pattern really does not have any indication on "character". No, I don't think we have any concrete reference as to how an empty string regex should be interpreted. By its nature, it should be the match of every possible zero-width position in the target CharSequence, which is char based upon the API. It might be desired to document this somewhere in the Pattern class. -Sherman On 06/08/2012 04:14 AM, Dawid Weiss wrote:
I guess a lot depends on the point of view. From historical point of view (where a char[] and a String are basically unsigned values) that pattern should simply process every value (index) and work like you say. But from a practical point of view I think it is a bug -- it corrupts the string, transforming legal unicode into invalid values.
I checked with Python (3) and the behavior there is the expected one (it work at the unicode codepoint level rather than surrogate level).
Where is the behavior of "" that you mention defined? I admit I couldn't find any reference to this in the documentation:
Using an empty String "" as a regex for the replaceAll() takes the advantage of the special meaning of "", in which it is interpreted as it can match any possible zero-width position of the target String I'm not saying you're wrong (and that pattern is definitely not common so it's probably academic discussion) but I'd like some concrete reference as to how an empty pattern should behave. To me consistency with the rest of the Pattern specification would be that it operates at "zero width position between unicode characters" not between any char[] value, even an incorrect one or in the middle of a surrogate.
Dawid
On Fri, Jun 8, 2012 at 12:46 AM, Xueming Shen<xueming.shen@oracle.com> wrote:
Personally I don't think it is a bug. A j.l.String represents a sequence of UTF-16 chars. While a pair of surrogates represents a supplementary character, a single surrogate itself is still a "legal" independent entity inside a String object and length of a String is still defined as the total number of char unit and an index value between a high surrogate and a low surrogate is still a legal index value that can be used to access the char at that particular position. Using an empty String "" as a regex for the replaceAll() takes the advantage of the special meaning of "", in which it is interpreted as it can match any possible zero-width position of the target String, it does not imply anything regarding "character" or "characters" around it, so I would not interpret it as a zero-with character boundary, therefor a "position" in between a pair surrogates is still a good "found" for replacing.
-Sherman
On 6/7/2012 1:07 PM, Dawid Weiss wrote:
Hi, I'm a committer to the Apache Lucene project. We have randomized tests and one seed hit the following (simplified) scenario:
String s1 = "AB\uD840\uDC00C"; String s2 = s1.replaceAll("", "X");
the input contains an extended unicode character (any surrogate pair will do). The pattern is an empty string (in fact, it was randomized as "]|" but it's the same problem so I omit the details). The problem is that after applying this pattern, replaceAll inserts X in between the surrogate pair characters and this results in invalid UTF-16:
AB𠀀C XAXBX?X?XCX
I believe this is a bug in the regexp implementation (sorry, don't have a patch for it) but I'd like to confirm it's not something known. Pointers appreciated.
Dawid